Canberrans sweated through our hottest night in nine years on Wednesday, with the mercury hovering in the mid-20s right through to sunrise on Thursday.

Weatherzone meteorologist Brett Dutschke described it as "very unusual" for this time of year.

"That's 14 degrees above average for this time of the year," Mr Dutschke said.

Residents of the capital were warned to brace for gale-force winds on Thursday morning with damaging gusts up to 80km/h expected.

The severe-weather warning was compounded by a high fire-danger rating.

The hot, hair dryer-like winds kept emergency services on their toes.

Wind gusts of 120km/h were reported from Thredbo's top station on Wednesday night, with conditions expected to deteriorate throughout the morning.

The State Emergency Service advised people to keep their cars under cover or away from trees.

Tidbinbilla Nature Reserve was closed because of high winds just before noon, but the Visitors Centre remained open.

Fire crews were called to Hawker about 7am after reports of sparking from a branch falling on power lines.

A bushfire flared up on the Monaro Highway between Cooma and Canberra, and another blaze at Turlinjah on the south coast shut down the Princes Highway in both directions for almost two hours.

A suspicious grass fire that flared up on Wednesday night in Canberra's Constitution Avenue was quickly doused by crews, including a couple of quick-thinking cops wielding a fire extinguisher.

"It looked like the peak of the winds would be in the middle of the day so lunchtime is not going to be very pleasant. It'll be not just the winds, they'll be picking up a bit of dust as well and the pollen will be flying around and blowflies coming in," Mr Dutschke said

Thursday night was expected to bring a bit of reprieve with winds set to drop off for a calm evening.

"Overnight we'll have wind turned a bit more easterly but it'll only be a light and brief change, which means it'll be quite chilly on Friday morning but it won't take long to warm up over the coming days," he said.

Light winds will caress the capital coming to the weekend for a mostly sunny, mild Friday and Saturday.

On Sunday the temperature will again stretch towards the high 20s, with the dry westerly winds set to return before next week.